The present invention relates to an ignition apparatus for an internal combustion engine and a one-chip semiconductor for this.
There is an ignition apparatus for an internal combustion engine described in Japanese Patent Application Laid-Open No. Hei 8-335522 as one prior art, in which a power switching part, a current limiting circuit acting as a protection circuit and a thermal shut-off circuit which compulsorily intercepts or blocks current flowing at the time of abnormal heat generation are integrated all together on an IGBT monolithic silicon substrate. Moreover, a suppression method is devised by setting up a collector clamping voltage to be tens of voltages, as a method of not generating high voltage at the secondary side of an ignition coil, at the time when compulsion turn the current off by the voltage generation of as many as the turn ratio times. There is an ignition apparatus for an internal combustion engine described in Japanese Patent Application Laid-Open No. Sho 53-118781 as another prior art. In this ignition apparatus, a hybrid IC equipped with electronic parts on a ceramic substrate etc. is used. This ignition apparatus has its function for dully intercepting the primary electric current due to the Miller integration effect using a capacitor by detecting the malfunction of the ignition signal.
The prior art as shown in Japanese Patent Application Laid-Open No. Hei 8-335522 has installed a current limit circuit and a thermal shut-off circuit in the igniter apparatus as security or protection function. However, when an element temperature becomes more than a set temperature, such a simple thermal shut-off circuit compulsorily makes the gate signal of the power transistor LOW, is generated high voltage by this operation at the ignition coil secondary side because it is the function to intercept the primary current which flows in the ignition coil quickly, and generates electrical discharge in the sparking plug. Therefore, there is a possibility to cause deleterious combustion like backfire, etc. according to the process of the engine. It is necessary not to generate a high voltage at the secondary side of the ignition coil to prevent this deleterious combustion at the compulsion turn the current off. A suppression method is devised by dropping the collector clamping voltage to tens of V as a simplest prevention method by the voltage generation of as many as the turn ratio times. However, it is usually undesirable to be necessary to operate by 24V+xcex1 of the battery series connection, and to adjust the collector clamping voltage to 30V or less as the ignition apparatus for cars. In case where the coil turn ratio of the ignition coil is 100 and the collector clamp voltage is 30V, for example, if the Vce voltage during the current limit is thought to be 7V, because the voltage of which value is turn ratio times of the collector voltage is generated at the secondary side of the ignition coil, the high voltage of 2.3 kV which is 100 times of 30Vxe2x88x927V=23V is generated. Spark discharge voltage generated at a spark plug differs depending upon the operating condition of the engine, and in case where pressure is high and air density thick, the spark discharge voltage is high, and conversely, in case where pressure is low and air density is thin, the discharge voltage is low. That is, because pressure goes up in the state to take a lot of air in the compression process of the engine, a high secondary voltage is demanded, and because negative pressure occurs in the state that air flow rate is small during the engine air suction process, spark discharge is generated at a low secondary voltage. High negative pressure is generated in case where the engine is operated at high speed and a throttle valve is closed rapidly when piston speed is high. This general value is Absolute Pressure 13-14 kPa (atmospheric pressure: 106.7 kPa). In case where the primary current is compulsorily blocked, since it is necessary for spark discharge not to be generated in any condition of the engine, so it is needed to suppress the secondary voltage to above such a value that spark discharge does not occur, even though the spark discharge can be easily generated by negative pressure. Especially, since when the engine shows negative pressure is in its suction process, igniting under such a condition causes the deleterious combustion of the engine such as backfire, etc. The one that the relation between negative pressure and spark discharge was found by the experiment is shown in FIG. 1. In this experiment, Sparking Plug F7LTCR made by BOSCH (GAP width: 1.2 mm) mounted in an aluminum chamber of which internal pressure is decreased by a outside negative pressure pump was used, and its pressure and the secondary voltage at which spark discharge generates at at that time were measured. 1a, 1b, 1c and 1d show discharge voltage waveforms at the time of the atmospheric pressure (106.7 kPa), 40 kPa, 20 kPa and 13 kPa, respectively. As is clear from the results of this experiment, the plug discharge voltage at the time of the absolute pressure of 13 kPa is 1.5 kV, so in order not to generate the spark discharge at the sparking plug it is needed to suppress the secondary voltage to under about 1 kV. Waveform 1e shows the fact that discharge does not occur at 1 kV even at the time of the absolute pressure 1.3 kV. This means that with the system in which said collector clump voltage is made to 330V, the plug discharge cannot be avoided.
Moreover, with the technology which prevents electrical discharge at the sparking plug by dully intercepting the primary electric current using the Miller integration effect with the capacitor and controlling a high voltage generated at the secondary side of the ignition coil, as shown in the above-mentioned Japanese Patent Application Laid-Open No. Sho 53-118781, to intercept the primary electric current dully to prevent the electrical discharge at the sparking plug, a capacitor with large capacity is needed. Therefore, making it on a silicon substrate is extremely disadvantageous in the size.
In order to settle the problems of the above-mentioned prior techniques, in accordance with this invention, when the collector current of a power transistor is blocked compulsorily at the time of abnormal heat generation, the collector current is changed so that the secondary voltage becomes under the plug discharge voltage in order not to generate spark discharge due to the secondary voltage generated at the secondary side of the ignition coil, said secondary voltage is generated repeatedly by repeating this control, and energy is emitted which has been charged in the ignition coil. Experiment waveforms on the desk of the circuit which achieves the present invention is shown in FIG. 2. It is understood from the waveforms to be able to obstruct deleterious ignition by no generating the plug electrical discharge because the generated secondary voltage is discharged repeatedly by 800V peak. Through the control of the gate voltage like this and the control of the amount of change of the primary electric current, it is possible to intercept compulsorily the primary electric current while controlling the voltage generated at the secondary side of the ignition coil to become 1 kV or less.
As means for generating repeating the secondary voltage below this plug discharge voltage, a digital control circuit which changes the collector electric current in a step way by using a pulse waveform is used. As a result, it is possible to form the control circuit easily on a silicon substrate without needing a capacitor with large capacity. Moreover, after compulsory interception is performed once, a latch circuit which does not carry out current flowing until the ignition control signal becomes LOW again is installed. As a result, abnormal current flowing operation is prevented by the control which does not provide the current flowing again, even if chip temperature becomes below a set value while generating the malfunction current flow. These control circuit components are integrated in the monolithic substrate of the power transistor.
As mentioned above, flying sparks to the sparking plug can be obstructed by controlling the gate voltage of the power transistor to intercept the electric current in a step way so that the secondary voltage generated at the secondary side of the ignition coil is suppressed below the plug discharge voltage when the ignition apparatus generates abnormal heat and intercepts the primary current compulsorily. By integrating these control circuits and power part on the monolithic silicon substrate of the power transistor, it is possible to provide a one-chip ignition apparatus of multi-function with high stability and reliability of operation.